A composite material (a composite) is formed by combining two or more materials that have different properties. The composite typically has properties different from those of its constituent materials, but within the composite the original materials can still be identified (they do not dissolve; an interface is maintained between them). Typically, one material, called the matrix, surrounds and binds together discrete units (e.g., particles, fibers, or fragments) of a second material, called the filler.
Many composite materials are currently known and widely used, for example, concrete (a composite in which the matrix is cement and the filler is aggregate), fiberglass (glass fibers in a plastic matrix), and many other types of reinforced plastics. However, there is continued demand for novel composites with desirable properties for many applications.
For example, the electronics industry utilizes materials that have high dielectric constants and that are also flexible, easy to process, and strong. Finding single component materials possessing these properties is difficult. For example, high dielectric constant ceramic materials such as ferroelectric SrTiO3, BaTiO3, or CaTiO3 are brittle and are processed at high temperatures that are incompatible with current microcircuit manufacturing processes, while polymer materials are very easy to process but have low dielectric constants. Composite materials with micron-scale ferroelectric ceramic particles as the filler in liquid crystal polymer, fluoropolymer, or thermoplastic polymer matrices are taught in U.S. Pat. No. 5,962,122 to Walpita et al (Oct. 5, 1999) entitled “Liquid crystalline polymer composites having high dielectric constant,” U.S. Pat. No. 5,358,775 to Horn et al (Oct. 25, 1994) entitled “Fluoropolymeric electrical substrate material exhibiting low thermal coefficient of dielectric constant,” U.S. Pat. No. 5,154,973 to Imagawa et al (Oct. 13, 1992) entitled “Composite material for dielectric lens antennas,” and U.S. Pat. No. 4,335,180 to Traut (Jun. 15, 1982) entitled “Microwave circuit boards.” However, these materials do not possess ideal processing characteristics. For example, they are difficult to form into the thin uniform films used for many microelectronics applications.
Novel materials would also be useful in other industries, for example, in solar energy technology. The development of solar energy technology is primarily concerned with reducing the cost of energy conversion. This is typically achieved in one of two ways: 1) increasing the conversion efficiency of light in a solar cell without proportionately increasing its cost, or 2) increasing the size of the cell without proportionately increasing its cost. In the first case, the same number of photons hit the solar cell, but a larger number of them are converted into electricity (or the ones that are converted are converted at a higher total power). In the second, the conversion efficiency is the same, but the larger surface area means that more photons are collected per unit time. Since the sun is free, this results in improved cost efficiency. Unfortunately, at the moment neither of these strategies is effective. The complexity of increased-efficiency solar cells causes their cost to be substantially greater than the increase in performance. Similarly, larger solar panels are proportionately more expensive due to difficulties in fabricating uniform devices over large areas.
Among other aspects, the present invention provides high dielectric constant nanocomposites that overcome the processing issues noted above and solar concentrators comprising nanostructures. A complete understanding of the invention will be obtained upon review of the following.